1. Field of the Invention
The present invention relates to a dog clutch type transmission suitable for use in a motorcycle or the like.
2. Background Art
A conventional dog clutch in a transmission includes a plurality of angular or round male dowels having the same height, and a plurality of female dowels adapted to engage the male dowels, thereby transmitting torque. This type of dog clutch is shown in Japanese Utility Model Publication Nos. Sho 59-4867 and Hei 4-22107.
Another conventional dowel structure has high male dowels and low male dowels of differing height, with the number of the female dowels being half the number of male dowels. Both the surface of each high male dowel and the surface of each low male dowel are machined. In this arrangement, a female dowel is a dowel hole or a recess adapted to engage a male dowel.
To increase the chance of engagement of the male dowels with the female dowels in the conventional dowel structure, the distance between neighboring ones of the male dowels must be increased, and each male dowel must therefore be reduced in size. However, the size reduction of each male dowel is limited because its strength must be sufficient. The ability to increase the chance of engagement is therefore limited in conventional devices.
In addition, in conventional devices, the play of each male dowel engaged with the corresponding female dowel must be adjusted in magnitude according to characteristics of individual types of transmissions, and the design of the male dowels is limited by the type of transmission in which it is utilitized. It is also necessary to set gears having different dowel specifications for manual and automatic transmissions.
The present invention overcomes the shortcomings associated with conventional devices and achieves other advantages not realized by conventional devices.
In one embodiment of the invention, a transmission shifts gears by engaging or disengaging a dog clutch, the dog clutch comprising a plurality of angular male dowels and a plurality of female dowels adapted to engage the male dowels. Each of the male dowels has a curved engaging surface, and each of the female dowels has a flat engaging surface for contacting the curved engaging surfaces.
A contact position between the curved engaging surface of each male dowel and the flat engaging surface of each female dowel is offset radially outward from a radial center of each male dowel. The male dowels comprise high male dowels and low male dowels that differ in height, and the high male dowels and the low male dowels are alternately arranged.
The number of female dowels is half the number of the male dowels. The tolerance of the height of each low male dowel is a maximum working tolerance by forging, and the surface of each low male dowel is an unmachined surface left after forging.
Each male dowel is angular, with its engaging surface formed as a curved surface. The engaging surface of each female dowel is formed as a flat surface. Accordingly, a pitch circle of engagement of the male and female dowels can be set, and a contact position between these engaging surfaces can be specified to a most effective position by adjusting the pitch circle.
The contact position between the engaging surfaces of the male and female dowels is offset radially outward by setting the pitch circle to thereby enlarge the radius of rotation of a contact portion between the male and female dowels. Accordingly, the contact portion is a thick-walled portion, and the strength of the male dowels can be ensured. Further, in a usual male dowel, stress concentration tends to occur at the root of a radially inner end of the male dowel. Accordingly, by radially outwardly offsetting the contact point, a stress portion can be spaced apart from the root of the radially inner end. As a result, the strength can be improved as compared with that of a conventional male dowel having a similar size.
The chance of dynamic engagement of the male and female dowels is determined by the start of engagement of these dowels. Accordingly, by alternately arranging the high male dowels and the low male dowels of differing height, the start of engagement is effected by the engagement of the high male dowels into the female dowels, thus ensuring the increased chance of engagement.
After completing the engagement of the high male dowels into the female dowels, the low male dowels are also engaged into the female dowels, so that the play determined after the engagement can be set to a small amount. Thus, the chance of engagement can be increased with the play reduced, and the degree of freedom of design can be increased. As a result, both a foot-operated gear change and a motor-operated gear change can be carried out by the same gear.
The maximum tolerance of the height of each low male dowel is set as a maximum working tolerance by forging. Accordingly, each low male dowel can be used as a forged part. Because the low male dowel is not machined, the number of production steps can be reduced, reducing costs.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.